$ { {-3} \times \left[\begin{array}{r}{1} \\ {-2} \\ {-1}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{-3}\times{1} \\ {-3}\times{-2} \\ {-3}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-3} \\ {6} \\ {3}\end{array}\right]}$